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I'm adding an exception here to allow disabling the feature like this. I am assured that existing tests are not affected by the default state of the flag. This will be evident as CI runs. @jesup will file follow-ups.

Harbormaster completed remote builds in B898414: Diff 1185760.Jan 16 2026, 5:16 AM

jesup mentioned this in D279240: Bug 2010739: Disable Compression Dictionaries.Jan 16 2026, 5:19 AM

jesup mentioned this in D279241: Bug 2010739: Disable Compression Dictionaries.

Closed by commit rFIREFOXAUTOLAND7ac3827200d5: Bug 2010739: Disable Compression Dictionaries r=mt (authored by jesup, committed by rjesup@mozilla.com <rjesup@mozilla.com>). · Explain WhyJan 16 2026, 5:21 AM

This revision was automatically updated to reflect the committed changes.

rjesup@mozilla.com <rjesup@mozilla.com> added a commit: rFIREFOXAUTOLAND7ac3827200d5: Bug 2010739: Disable Compression Dictionaries r=mt.

pchevrel@mozilla.com <pchevrel@mozilla.com> mentioned this in rFIREFOXBETA9a422459a7c3: Bug 2010739: Disable Compression Dictionaries a=pascalc.Jan 16 2026, 7:42 AM

pchevrel@mozilla.com <pchevrel@mozilla.com> mentioned this in rFIREFOXRELEASEa7dd9359671c: Bug 2010739: Disable Compression Dictionaries a=pascalc.

sstanca reopened this revision.Jan 16 2026, 7:50 AM

This revision is now accepted and ready to land.Jan 16 2026, 7:50 AM

sstanca added a reverting change: rFIREFOXAUTOLANDb74fc4aba62e: Revert "Bug 2010739: Disable Compression Dictionaries r=mt" for causing wpt….Jan 16 2026, 7:50 AM

dholbert added a parent revision: D279260: Bug 2010762: Annotate WPT decoded-body-size-compressed.https.html as needing compression dictionaries pref to be enabled. r?mt.Jan 16 2026, 8:45 AM

dholbert removed a parent revision: D279260: Bug 2010762: Annotate WPT decoded-body-size-compressed.https.html as needing compression dictionaries pref to be enabled. r?mt.

Re-triggering lando - this should be good to land on top of https://phabricator.services.mozilla.com/D279260 (which I just separately triggered lando for)